1b.Approach (from AD-416):
Populations of watermelon segregating for resistance to Phytophthora fruit rot will be generated by crossing a highly resistant selection developed from a Citrullus lanatus var. lanatus accession with susceptible commercial cultivars of C. lanatus. These populations will be phenotyped for reaction to Phytophthora fruit rot to determine inheritance of resistance. Molecular markers closely linked to resistance genes will be identified and used in marker assisted selection (MAS) to develop fruit rot resistant breeding lines. Breadth of resistance in watermelon germplasm and breeding lines will be assessed against isolates of Phytophthora capsici from several Southeastern states. Advanced watermelon germplasm lines resistant to vine decline (caused by the whitefly-transmitted squash vein yellowing virus, SqVYV) will be developed using known sources of resistance to SqVYV in wild watermelon accessions via the pure line selection breeding procedure. The advanced resistant germplasm will be crossed with a susceptible commercial cultivar to develop segregating populations to determine inheritance of resistance to SqVYV. Genetic populations of wild watermelon (Citrullus lanatus var. citroides) segregating for resistance to southern root-knot nematode (RKN, Meloidogyne incognita) will be developed and phenotyped for reaction to RKN to determine the mode of inheritance of resistance. Molecular markers closely linked to the RKN resistance gene(s) will be identified and used for gene mapping and MAS. Watermelon populations segregating for resistance will be developed by crossing RKN-resistant C. lanatus var. citroides with cultivated watermelon, C. lanatus. These populations will be phenotyped for reaction to RKN and MAS utilized to develop RKN-resistant watermelon breeding lines. Sweet peppers (sweet banana, sweet cherry, and Cubanelle types) with resistance to southern RKN will be developed using conventional recurrent backcross breeding procedures to transfer the dominant ‘N’ gene for RKN resistance from resistant bell pepper to sweet pepper. Genetic populations of pepper (Capsicum annuum) segregating for resistance to northern RKN (M. hapla) will be developed by crossing a highly resistant selection from a C. annuum accession with a susceptible commercial C. annuum cultivar. These populations will be phenotyped for root galling and RKN reproduction to determine mode of inheritance of resistance to northern RKN.

3.Progress Report:
Several new Phytophthora fruit rot resistant watermelon accessions were identified and resistant germplasm was developed. A release notice describing the four new fruit rot resistant lines was published. Crosses between Phytophthora fruit rot resistant and susceptible plants were made to develop populations for inheritance studies. Similar crosses made in 2011 were evaluated for fruit rot in 2012 and highly resistant lines with red flesh were selected for further evaluation.

Over 1,300 Plant introductions were screened and new sources of resistance were identified for possible use in managing the whitefly transmitted Squash Vein Yellowing Virus (SqVYV), which has caused devastating losses to the watermelon industry in Florida. Single plant selections from SqVYV resistant wild watermelon accessions were made to develop resistant watermelon germplasm. A release notice for a new germplasm line, 392291-VDR, was published. Crosses between 392291-VDR and susceptible ‘Charleston Gray’ and ‘Mickey Lee’ were made to develop populations for conducting inheritance studies.

Strategies to manage white-fly transmitted viral watermelon vine decline (WVD) including insecticide treatments and resistant pollenizers were developed and experiments were completed. Vine decline resistant pollenizers reduced WVD on the foliage and fruit of the susceptible seedless watermelon Tri-X 313 compared to the susceptible pollenizer ‘Mickey Lee’. Large scale trials conducted in fall 2012 in Immokalee, FL, confirmed these findings.

Watermelon lines were developed and selected for resistance to root-knot nematodes (RKN). The most resistant watermelon lines were evaluated as rootstocks for managing RKN in grafted seedless watermelon in field trials. Several watermelon rootstocks exhibited significantly higher resistance to RKN than squash hybrid and bottle gourd rootstocks, which are commonly used for grafted watermelon.

Homozygous lines of sweet cherry, Cubanelle, and sweet banana were selected for resistance to southern RKN, Meloidogyne incognita, and back-crossed to susceptible parents in order to recover fruit types of the original parents. The most resistant sweet cherry pepper lines are being evaluated for fruit characteristics and fruit yields in field tests.

Advanced sweetpotato breeding lines from USDA, Charleston, North Carolina, and Louisiana, entered in the Sweetpotato Collaborator’s Test were evaluated for resistance to southern RKN, M. incognita. Sweetpotato seedlings from USDA, Charleston, SC were screened for resistance to RKN in efforts to develop RKN resistant sweetpotato varieties.

The most resistant African horned cucumber (Cucumis metulifer) accessions from the U.S. Plant Introduction (PI) collection (identified in previous tests) were evaluated for resistance to RKN (M. incognita) in field tests. Ten African horned cucumber lines selected for resistance to RKN were re-evaluated as rootstocks for grafted ‘Athena’ cantaloupe in RKN-infested fields. Several C. metulifer rootstocks grafted with ‘Athena’ cantaloupe produced higher fruit yields than non-grafted ‘Athena’ and ‘Athena’ grafted on ‘Carnivor’ squash hybrid rootstock.

4.Accomplishments
1.
Phytophthora fruit rot resistant watermelon germplasm lines. Phytophthora fruit rot is a serious disease that has plagued watermelon growers in the eastern U.S. for the past several years. The disease is especially severe in GA, SC, and NC. ARS scientists developed four watermelon germplasm lines (USVL489-PFR, USVL782-PFR, USVL203-PFR, and USVL020-PFR) with resistance to Phytophthora fruit rot. These resistant germplasm lines can be used by breeders to develop watermelon varieties with resistance to this dreaded disease. Development of such varieties will help growers reduce fungicide use and allow them to produce a successful crop free of fruit rot.